Method of forming a low-k layer in an Integrated circuit

ABSTRACT

This is a device and method of forming such, wherein the device has an amorphous &#34;TEFLON&#34; (TFE AF) layer. The device comprising: a substrate; a TFE AF 44 layer on top of the substrate; and a semiconductor layer 42 on top of the TFE AF 44 layer. The device may be an electronic or optoelectronic device. The semiconductor layer may be a metal or other substance.

This application is a continuation of application Ser. No. 08/483,422filed Jun. 7, 1995, now issued as U.S. Pat. No. 5,824,603, which is adivisional of application Ser. No. 08/148,779, filed Nov. 5, 1993, nowissued as U.S. Pat. No. 5,468,561.

FIELD OF THE INVENTION

This invention is directed towards the field of fabrication ofelectronic and optoelectronic components.

BACKGROUND OF THE INVENTION

As device geometries continue to decrease in electronics andoptoelectronics, capacitance density will increase and the peformance ofintegrated circuits will be limited by the high RC time constants causedby high resistivity metals and high capacitance interlevel dielectrics(ILD). Reducing the dielectric constant of the interlevel insulator willnot only enhance performance, but also decrease the power consumptionand crosstalk of electronic/optoelectronic devices.

For a given interconnect layout, both power dissipation and crosstalkdecrease as the dielectric constant of the insulator decreases. FIG. 1shows the power dissipation of 0.25 μm and 0.50 μm metal lines whendifferent ILDs are used. The data show that using the same dielectric,scaling down from 0.50 μm to 0.25 μm will result in a 30% increase inpower dissipation. The power dissipation can be decreased more than 50%if SiO₂ ILD is replaced by a copolymer made from tetraflouroethylene and2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (TFE AF). (TFE AF iscommercially available from "DU PONT" in a product known as amorphous"TEFLON"; "TEFLON" is a polymer made from polytetrafluoroethylene (PTFE)also commercially available from "DU PONT"). This change is particularlyimportant for high frequency operation because power dissipationincreases proportional to frequency. The power consumption can befurther reduced if a metal of lower resistance, such as Cu, is used toreplace current metalization materials such as Al or W.

FIG. 2 shows the crosstalk between 0.25 μm and 0.5 μm metal lines whenthe power supply voltage (V_(cc)) is 1 V. The crosstalk increases morethan 50% when the design rule is reduced from 0.5 μm to 0.25 μm,primarily due to the increase in line-to-line capacitance. The increasein crosstalk/V_(cc) ratio degrades the noise margin and hence circuitperformance. Replacing SiO₂ by TFE AF will significantly reducecrosstalk.

Several material properties are required for a successful low-ε_(r)technology. These include: 1) low dielectric constant k, 2) highmechanical strength, 3) good thermal stability, 4) high dielectricstrength and low leakage current, 5) low stress, 6) good adhesion, 7)good gap filling capability/ease of planarization, 8) ease of patternand etch, 9) low water absorptivity, 10) good etch selectivity to metaland 11) good thermal conductivity. A list of a few important propertiesof TFE AF, PTFE and SiO₂ are given in Table 1. The properties of PTFEand SiO₂ are listed for comparison.

                  TABLE 1                                                         ______________________________________                                        Requirements  TFE AF     PTFE      SiO.sub.2                                  ______________________________________                                        Dielectric Constant k                                                                       1.9        2.1       3.5-4.0                                      Dissipation Factor <0.00035 <0.0002 0.001                                     Stable Temperature 360° C. 380° C. 1600° C.                                                Creep Resistance good poor good                                               Resistivity (ohm-cm) >10.sup.18                                              >10.sup.18 10.sup.14-17                      Dielectric Strength 0.2 (MV/cm) 1.3 5-8                                       Thermal Conductivity   0.012                                                  Chemical Resistance excellent excellent                                       Water Absorption <0.01% <0.01%                                              ______________________________________                                    

No single polymer exhibits all of the required characteristics. TFE AFhas the lowest dielectric constant in known polymers. In addition, TFEAF has processing advantages.

Unlike PTFE, which is formed by molding, TFE AF can be deposited as athin film by either spin-coating, thermolysis or laser ablation. Thismakes it more applicable to integrated circuits. TFE AF exhibits bettercreep resistance, a lower dielectric constant, lower thermal expansionand higher tensile strength than PTFE. Good chemical resistance and lowwater absorption are common for both materials.

SUMMARY OF THE INVENTION

TFE AF films can be deposited on Al, SiO₂, Si₃ N₄, Si and other materialsubstrates by spin-coating, using TFE AF. The thickness of the films canbe varied from <5 nm to >1200 nm by diluting the TFE AF solution withFluorinert FC-75 (made by "3M"). In addition, the thickness of the filmscan be controlled by using different spin speeds. Initial resultsindicate all films on the above-listed substrates pass the Scotch tapetest. In contrast, films deposited on the TFE AF layers tend to peel offduring subsequent processing. In fact, the TFE AF surface is sonon-sticky that photoresist could not be put on by spin-coating. Inaddition to the problem of putting on patterned photoresist, the TFE AFfilms have to be etchable. However, since the TFE AF has good chemicalresistance, it is difficult to etch by wet chemicals. Finally, since thesurface of a spin-coated TFE AF films is wavy, it may be necessary toplanarize the films by an etch-back process. That also demands anetching process.

Accordingly, improvements which increase the patternability, etchibilityand adhesion of TFE AF are presently desirable. The present invention isdirected towards meeting those needs.

Although wet chemical is of little use in etching the TFE AF film, dryetching is found to be very efficient. The TFE AF films have been etchedin Ar, O₂ or CF₄ +O₂ plasma gases effectively. Dry etching alsoincreases the surface roughness of the TFE AF films. The increasedsurface roughness and a possible chemical change on the TFE AF films,making it suitable for photoresist spin-coating and patterning. Inaddition, adhesion to other materials deposited over the TFE AF has beenincreased.

This is a device and method of forming such, wherein the device has aTFE AF layer. The device may comprise: a substrate; a TFE AF layer ontop of the substrate; and a material layer on top of the TFE AF layer.The device may be an electronic or optoelectronic device. The materiallayer may be a metal or other substance.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further aspects of the invention are illustrated inthe accompanying drawings wherein like elements are denoted by likereference designators and in which:

FIG. 1 is a graph of the power dissipation of 0.25 μm and 0.50 μm metallines when different ILDs are used;

FIG. 2 is a graph of the crosstalk between 0.25 μm and 0.5 μm metallines when the power supply voltage (V_(cc)) is 1 V;

FIG. 3 is a micrograph of the change in contact angle for water dropletson as-deposited and plasma-etched TFE AF;

FIG. 4 is a micrograph of a Al/TFE AF/Al/Si(100) capacitors built inaccordance the invention;

FIG. 5 is a micrograph of the edge of the capacitor in FIG. 4;

FIG. 6 is a microgrph of a TFE AF mesa built in accordance with theinvention;

FIG. 7 is micrographs of as-deposited and plasma-etched TFE AF filmsstudied by atomic form microscopy (AFM); and

FIG. 8 is Cls spectra of as-deposited, plasma-etched, and Ar-ionsputtered TFE AF films.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Dry etching was performed in a plasma etcher (by Technics) with theprocess pressure at 350 mtorr and input power of 50 W. At thesesettings, the etching rates of TFE AF in Ar, O₂ and CF₄ (8%)+O₂ are 100,500, and 500 nm/min, respectively. Although Ar, O₂ and CF₄ (8%)+O₂ gaseshave been used effectively, O₂ demonstrated superior results. The etchedTFE AF surface was characterized by atomic force microscopy (AFM), andx-ray photoelectron spectroscopy (XPS). These investigations showed thatplasma etching created a rough surface and induced chemical changes inthe film surface. The increase in surface roughness promotes adhesion,and makes it possible to spin-coat photoresist with adequate uniformityand full coverage on the etched TFE AF films. The chemical changes,along with increased surface roughness increases the adhesion of othermaterials (such as Al, TiW, etc.) to TFE AF. FIG. 3 shows the change incontact angle for water droplets 32 on an as-deposited 30 and aplasma-etched 34 TFE AF film. The smaller contact angle of water andphotoresist solution on the plasma-etched TFE AF film indicates thatadhesion of water and photoresist solution on the TFE AF film has beenincreased. Although photoresist can not stay on an as-deposited TFE AFfilm by spin-coating, uniform and fully covered photoresist can beachieved on a plasma-etched TFE AF film. The photoresist-covered TFE AFfilms can then be patterned and etched by standard lithographyprocesses.

This patterning process was successfully used to fabricate Al/TFE AF/Alcapacitors and TFE AF mesa structures. The procedure is used tofabricate the Al/TFE AF/Al/Si(100) capacitors shown in FIG. 4. Tofabricate the Al/TFE AF/Al capacitors, a photoresist layer was firstspin-coated on plasma-etched TFE AF 40 over Al 40 and Si(100). Thephotoresist was exposed to UV light and developed to form a patternedphotoresist film on the TFE AF layer. An Al film 42 was then depositedon the patterned photoresist and the exposed area of the TFE AF layer44. After lifting off the photoresist, the Al dots 42 on the TFE AF 44was used as masks during the following CF₄ /O₂ plasma etching. Theplasma etching removed exposed TFE AF and stopped at the Al layer 40underneath the TFE AF film 44. The edge of a capacitor in FIG. 4 isshown in FIG. 5. The same patterning process can be used to form TFE AFmesa as shown in FIG. 6. FIG. 6 shows TFE AF 48 over Al 46. In addition,materials (such as Al, TiW, etc.) can then be deposited over thepatterned TFE AF because the adhesion has been increased.

FIG. 7 shows micrographs of as-deposited and plasma-etched TFE AF filmsstudied by atomic form microscopy (AFM). It is clearly shown that thefilm etched in plasma is rougher than the as-deposited film.

FIG. 8 shows that the effects of plasma-etching on the chemical bonds ofTFE AF are similar to those of Ar-ion sputtering. New chemical bonds areformed, as indicated by comparing the two spectra with the spectrum ofas-deposited TFE AF.

Using these methods to deposit photoresist and etch TFE AF films, trenchlines and via holes can be patterned in TFE AF films. In addition,patterned metal/insulator/metal/semiconductor structures can befabricated with TFE AF as the insulator. Current-voltage andcapacitance-voltage measurements of the TFE AF capacitors showed lowleakage current and a relative dielectric constant of 1.9.

It should be noted that although TFE AF shows excellent resistance towet chemicals, it can became unstable when it contacts Al duringperoxide etching. It is believed that Al acts as a catalyst in this caseand makes TFE AF react with peroxide.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method of forming a low-k layer in an integrated circuit, comprising:depositing a low-k layer comprising a tetrafluoroethylene/2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxol copolymer on a partially completed integrated circuit, wherein the low-k layer has an exposed face; dry etching the exposed face of the low-k layer; depositing a photoresist layer on the etched, exposed face of the low-k layer; patterning the photoresist layer to expose portions of the low-k layer; depositing a mask layer on the patterned photoresist layer and exposed portions of the low-k layer; removing the patterned photoresist layer and the portions of the mask layer overlying the patternened photoresist layer; and dry etching the integrated circuit to remove the low-k layer except in areas underlying the mask layer, whereby a patterned low-k layer is formed.
 2. The method of claim 1, wherein dry etching the exposed face comprises plasma etching.
 3. The method of claim 1, wherein dry etching the exposed face comprises plasma etching in an atmosphere selected from the group consisting of Ar, O2, and combinations of CF4 and O2.
 4. The method of claim 1, wherein dry etching the exposed face comprises plasma etching in an O2 atmosphere.
 5. A method of forming a low-k layer in an integrated circuit, comprising:depositing a low-k layer comprising tetrafluoroethylene on a partially completed integrated circuit, wherein the low-k layer has an exposed face; roughening the exposed face of the low-k layer to increase the face's ability to adhere; and forming a layer of material on the roughened face of the low-k layer; wherein the layer of material is a masking layer comprising photoresist.
 6. The method of claim 5, wherein the low-k layer is amorphous.
 7. The method of claim 5, wherein the low-k layer comprises a tetrafluoroethylene/2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxol copolymer.
 8. The method of claim 6, wherein roughening the exposed face comprises dry etching.
 9. The method of claim 6, wherein roughening the exposed face comprises plasma etching.
 10. The method of claim 6, wherein roughening the exposed face comprises plasma etching in an O2 atmosphere.
 11. The method of claim 6, wherein roughening the exposed face comprises Ar-ion sputtering. 